1. Field of the Invention
This invention relates to an image heating apparatus typified by a fixing device used in an image forming apparatus such as a copier or a printer.
2. Related Background Art
Such a fixing device as is used in an image forming apparatus has a heating member for heating a recording material, a pressurizing member cooperating with the heating member to form a nip for nipping and conveying a recording material bearing an image thereon, and electrical energization controlling means for controlling the electrical energization of the heating member so that the heating member may maintain a set temperature, and heats the image by the thus temperature-controlled heating member to thereby secure good fixativeness of the image.
The heating member continues to be temperature-controlled when a plurality of recording materials are continuously heated as well as when a recording material is heated and therefore, during the time from after a recording material has passed through the nip until the next recording material enters the nip, the electrical energization of the heating member is effected to restore the temperature of the heating member which is reduced by the recording material taking away the heat quantity of the heating member, to a set temperature.
However, if the time from after a recording material has passed through the nip until the next recording material enters the nip is long, the temperature of the pressurizing member sometimes rises to a considerable temperature by the heat from the heating member of which temperature is continuously controlled during that time.
The inventor has found the phenomenon that if particularly the environment in which the apparatus is used is at a high temperature when the next recording material has entered the nip in a state in which the pressurizing member has thus risen in its temperature, the moisture contained in the recording material is evaporated by the heat of the heating member and adheres to the surface of the pressurizing member. The inventor also found the phenomenon that the recording material slips by the moisture adhering to the surface of this pressurizing member and the recording material fails to be normally conveyed and is jammed.